Filter block



FIG. 1 is a top plan view of the new and ornamental design for a filter block;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a cross sectional view thereof, taken along section line 4—4 of FIG. 1;

FIG. 5 is a side elevation view thereof; and,

FIG. 6 is a cross sectional view thereof, taken along section lines 6—6 of FIG. 1. parallel to the side view thereof. 

The ornamental design for a filter block, as shown and described. 